1. Field of the Invention
The present invention relates to a multiple-input multiple-output (MIMO) wireless communication method and system, especially to a MIMO wireless communication method and system capable of improving data throughput.
2. Description of Related Art
In wireless communication, multiple-input multiple output (MIMO) is a technology to use multiple antennas at both of the transmission and reception ends for communication performance improvement. The MIMO technology can greatly increase the data throughput, and therefore some modern wireless communication standards such as IEEE 802.11n, Long Term Evolution (LTE), Worldwide Interoperability for Microwave Access (WiMAX), and etc. adopt MIMO as an important part to carry out communication. However, in consideration of the interference caused by multiple devices transmitting simultaneously, the communication standard using MIMO (e.g. IEEE 802.11n) also adopts a Carrier Sense Multiple Access (CSMA) protocol to verify the absence of other transmission before transmitting on a shared radio channel. Through CSMA, a transmitter can determine whether any other transmission is in progress by the feedback of a receiver, and thereby avoids a potential collision or interference. To determine the winner among a plurality of transmitters running after the same transmission opportunity, a contention-based protocol is adopted, which allows many transmitters of different users to use the same radio channel without pre-coordination. For example, a transmitter in compliance with IEEE 802.11n standard under such a contention-based protocol will use a backoff counter to count down, and earn the opportunity to transmit when the backoff counter reaches zero provided that the intended radio channel is clear in the meantime.
As the MIMO technology is widely deployed in wireless communication devices (e.g. those conforming to IEEE 802.11n standard) and the capability of these devices moves on, a potential waste of transmission resources is observed. In some circumstances, a receiver capable of resolving spatial streams from different transmitters at the same time is forced to rest some of its hardware or software resources due to the concern of interference and the limit of the present protocol. In other words, a current MIMO wireless communication system only allows one winner among a plurality of transmitters pursuing the same transmission opportunity to transmit at a time. If such the concern or limit could be eliminated, the data throughput of the MIMO system could be raised significantly.